There is a decolorizing color material including an decolorizing function in which an image formed on a sheet of paper is decolorized using an external stimulus such as light having a specific wavelength, pressure and heating. In an electrophotographic image forming apparatus, a decolorizing toner as a decolorizing color material is transferred on a sheet of paper and is fixed by heat and pressure using a fixing device. Thus, an image is decolorized by applying pressure to and heating a decolorizing toner image at a decolorizing temperature higher than a fixing temperature and the sheet of paper may be reused.
However, in a sheet of paper to be reused, the image such as letter is erased from an image forming section of the sheet of paper and is not directly visible by human eyes. However, a resin configuring the decolorizing toner remains practically in the same state.
Thus, an adhesion quantity of decolorizing toner, which is adhered on the same portion on the sheet of paper, increases with an increase in the number of times of reuse sheet of paper. When the toner resin adhesion quantity formed on a sheet of paper increases, there is an effect on image formation such as transfer efficiency when transferring a toner image to the sheet of paper and fixing efficiency when fixing the toner image to the sheet of paper.
Accordingly, when the toner resin adhesion quantity that is present on a sheet of paper may be estimated before an image is formed on the sheet of paper to be reused, control targets related to the sheet of paper and the toner such as a transfer bias according to the toner adhesion quantity and a fixing temperature are controlled and reliable image may be provided.